Online advertising (typically banner advertisements) directed to Web users or subscribers has grown rapidly along with the growth of the Internet and e-commerce activity. Web advertising is frequently targeted to particular Web users. For example, it is known to profile Web users by determining their demographics and interests, and to selectively transmit advertisements to only those users having particular desired profiles. Information on users may be obtained from the users themselves through questionnaires or from other profiling techniques.
Online content delivery services typically contract with advertisers to deliver some specified number of advertisements (i.e., impressions) to Web users having particular profiles. In scheduling the delivery of advertisements, a number of variable factors are involved such as, e.g., when a given user will log on or for how long. Accordingly, the content delivery services typically pre-schedule all content deliveries for all users using very conservative estimates of scheduled deliveries in order to fulfill advertising contracts. Known content delivery systems are thereby very inefficient in utilizing inventory (available user screen real estate) and fulfilling advertiser contracts.